Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2017

Compensation Expense Related to Stock-Based Compensation Plans

The compensation expense related to the Company’s stock-based compensation plans included in the accompanying Consolidated Statements of Operations was as follows (in thousands):



	Three months ended June 30,				Six months ended June 30,
	Three months ended June 30,				Six months ended June 30,
	2017		2016		2017		2016
Cost of sales	$	107	$	134	$	237	$	369
Research and development	404		344		816		641
Sales and marketing	437		332		907		269
General and administrative	1,190		1,296		2,099		2,807
Total stock-based compensation expense	$	2,138	$	2,106	$	4,059	$	4,086

Estimated Fair Value of Each Stock Option Award

The estimated fair value of each stock option was determined on the date of grant using the Black-Scholes option valuation model with the following weighted-average assumptions for the option grants.



	Six months ended June 30,
	Six months ended June 30,
	2017		2016
Risk-free interest rate	2.31	%	1.47	%
Expected option life (in years)	6.63		6.59
Volatility rate	36	%	36	%
Dividend rate	—	%	—	%